have a question about the engine noise

Since you have no direct control over engine speed, and since the Prius is a smart car that optimizes its performance, don't worry about it. An ICE has more power at higher revs. If your foot on the pedal is calling for a lot of power, the ICE should rev high, as well as the electric motors sucking down the battery.

On the other hand, hard accelleration really lowers your fuel economy, so many people avoid the practice.

 

I noticed that also when I test drove the Prius under full throtle acceleration. I am not sure if it is an insulation issue with the engine compartment. Also keep in mind that you have a small engine under the hood that will scream when pressed hard. It is quite normal. Too bad there is no tachometer to see the engine rpms. I had the same experience when I test drove the Scion Xa.

 

The noise is normal. The Prius has a CVT type tramsmission so RPM does not relate to driving in the same way as a non-CVT car. This renders tachs nearless useless, but the MFD gives us far more useful information for this type vehicle.

 

With the eCVT, the engine speed does not correlate with the speed of the car, but with the power/load demands of the road and accelerator pedal.

Think of it like you riding a 1-speed bicycle - going downhill, you'd coast. going along a flat area, you don't need to pedal very hard to maintain speed, and you'd coast a bit. Going up a hill, you'd need to pedal a lot and huff and puff.

Don't worry about the sound of the engine - if you are accelerating hard or going up a hill (or worse, doing both), you'll probably get the engine at max RPM (which isn't red-lined, but is rev-limited to 4500RPM in the Classic and 5000RPM in the 2004-? Prius) and some electric to boost. If you are going downhill, it's very likely that the gasoline engine will shut off (or at least not be burning fuel).

It is a 4-cyl engine, after all. a few Classic Prius owners have added soundproofing to their engine compartments (such as a lining under the hood/bonnet), so that's an option if it really bothers you, but it is perfectly natural.

Actually, a number of people on test drives, if not forwarned, can accuse the Prius of being "slow" because of the disconnect between the sound of the engine and the speed of the car... (Floor the accelerator, the engine roars, person gets scared that they're hurting the engine and instinctively let off of the accelerator, and of course the car listens to the driver's pedal controls and slows down...)

 

It will sound like a slipping clutch/torque converter. But in reality, all electro/mechanical components are engaged at all times, so rest assured, nothing is slipping. What kinetic energy doesn't get directly to the wheels is transmitted to a generator (MG1) and the resulting electrical energy is fed back to the wheel motor (MG2), possibly being supplemented by the battery. If you look on the energy flow screen, you can see the orange(yellow) arrows going from the engine, to the generator, to the wheels, as well as a ruddy arrow flowing from the engine directly to the wheels. This is done by the power split device (PSD).

 

Agreed. When you feel frisky, just mash the pedal to the floor and watch the world fall behind.